Thermometric carbon composites

ABSTRACT

A composition of electrically conductive composites for temperature sensing comprises conductive particles. The composite forms from a suspension. The suspension comprises the particles and solvent, and the particles are conductive particles with aspect ratio larger than one. The conductive composite retains a negative temperature coefficient when in contact with certain specific surfaces. The particles within the composite self align.

CROSS-REFERENCES TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.60/746,638 filed May 6, 2006 (Anchor Science Ref. No.: AncSci001)“Thermometric Carbon Coatings” which is hereby incorporated by referencein its entirety.

BACKGROUND

The present invention is generally directed to carbon nanotube—graphenecomposites, their composition, and their use as temperature sensingelements in devices and articles, especially printable devices andarticles of any size including microelectromechanical systems andnanoelectromechanical systems. Graphene is a single planar sheet ofsp²-bonded carbon atoms. Parallel-oriented stack of graphene sheetsconstitutes graphite. A single wall carbon nanotube (SWCNT) is agraphene sheet rolled into a cylinder. A multi wall carbon nanotube(MWCNT) comprises of multiple graphene sheets rolled into concentriccylinders or a graphene sheet rolled into a scroll or multiple graphenesheets rolled into concentric scrolls.

The temperature measurement is a fundamental and ubiquitous necessity.The temperature dependence of electrical resistance of conductivecarbons, for instance, solid graphite [Bedford & Quinn] has been longknown and utilized for fabrication of thermometers functioning wellbelow ambient temperature in the cryogenic range. The thermometric useof graphite has been limited to low range of temperatures because ofproblems relating to nonunique temperature responses and low resistivityexhibited by these materials near the ambient temperature. Carbonresistors have been used as resistive thermometers as well but theirapplicability is also limited to low temperatures for reasons of thermalinstability, limited range of unique responses and sensitivity. Thesedevices also exhibited nonuniformity of properties relating tocomposition and thermal treatment history requiring repetitiveindividual calibration. Carbon-glass resistive sensors exhibit goodstability and monotonic change in resistance characteristic between 1.4K and 325 K, but their reduced sensitivity (0.01 Ohm/K) above 100 Klimits their usage at higher temperatures.

In case of nanodevices, the size is an essential feature. The global orremote temperature reading might not accurately reflect potentiallypresent local variation. It is eminently important to measuretemperature while using nanosensors, particularly carbon nanotube basedsensors as their responses are susceptible to temperature interference.It is requisite for the temperature sensor to be of the similar size asother sensors in a set of sensors or a sensor array. If known, thetemperature effect on other nano devices could be compensated for in thedevice calibration, improving the device's accuracy and reliability.

The need for temperature measurement on that scale is well appreciatedyet, serious practical difficulties persist. Metal nanowires are usedfor temperature mapping at low (cryogenic) temperatures [Nalwa].However, the nanowires exhibit positive temperature sensitivitycoefficient and their stability is questionable. Recently gallium filledCNT thermometer [Gallium] has been developed for temperature range from50 ° C. to 500 ° C. As the melting point of gallium is at about 29.78°C., gallium nanothermometer is inapplicable to bionanosensors. Anotherserious drawback of this thermometer is the use of transmission electronmicroscope for readout precluding portability of the device and severelylimiting its affordability. Operating in narrower T range light emittingnanothermometer has been demonstrated by Lee, Kotov and Govorov [Lee2005], but it is inapplicable to measuring temperatures of hidden fromview objects.

The use of carbon-based inks is common in the manufacture of printedelectronics, for example printed circuit boards or electrodes forsensors. In general, carbon-based ink is a composite material containinga carbon particulate such as graphite, amorphous carbon or a fullerene,suspended in a binder and a solvent. These composite materials areapplied to a surface via a number of deposition techniques, and thencured that is allowed to dry, or are subjected to accelerating orenhancing curing treatment. Conductivity enhancing curing usuallyconsists of heat treatment from 50 ° C. to several hundred degreesCelsius. Non-thermal curing has also been demonstrated [Kirkor]. Thecuring step is necessary to attain high conductivity in the resultingcarbon composites. After thermal curing, the material's conductivity istemperature dependent.

On any size scale, an unmanaged temperature dependence of conductivityof carbon based circuits integrated into functional blocks andapplications can limit the usefulness of finished products.

Materials with unique temperature signatures, operational ranges higherthan carbon-glass composites, and that are compatible with printableelectronics are needed. Use of graphenic carbon nanoparticles in aconductive carbon composite allows for scaling down the dimensions ofthe device as well as biological and chemical compatibility. An examplehere is the expanding presence of carbon nanotube sensors within thegrowing field of sensors and sensor arrays in the whole range of sizespresent. In this type of sensor, a reagent specific to a given analyteis carried by a carbon conductor (E.g., Carbon Nanotube or an ensembleof Carbon Nanotubes) to make a sensing element specific to the analyteof interest. Typically, the analytical response is temperaturedependent. Without temperature compensation, such devices are limited tooperation in a narrow temperature range.

In the field, sensors are often subjected to temperature changes. Commontemperature changes occur in the range from −80° C. to near 100° C., themost frequently measured temperature range. It is thus advantageous tomeasure temperature in that range and also on a similar scale as that ofthe size of the sensor.

The use of individual carbon nanotubes as thermometers could be possiblewith individual calibration. However, electrical properties of carbonnanotubes vary dependent on their internal structure and derivatization[Avouris, Gruner] rendering individual calibration so cumbersome andcostly that it is impracticable.

Individual cohesive bundles of parallel MWCNT under high vacuum exhibitmonotonic dependence of conductivity on temperature in range from 100 to800 K [Zhou 2004] . Similar behavior was reported for isolatedgraphite-metal contacts [Shklyarevskii 2005]. The electrical resistanceof ensembles of carbon nanotubes depends on chemical exposure oftenleading to disparately different and often non-monotonic temperaturedependence of the electrical properties. The phenomenon is evident bycomparison of results from numerous researchers [Kaiser 1998], [Hecht2006]. Given observed variability of conductivity of CNT containingmaterials, properties of individual components cannot be expected ofintermixed composite materials. Thus, carbon nanotubes typically havenot been used for temperature sensors.

SUMMARY

In a first aspect, the present invention is a composition of a mixtureof the carbon particles comprising tubular carbon particles and theplanar carbon particles in a temperature sensing layer. The tubularcarbon particles comprise single wall carbon nanotubes or multiple wallcarbon nanotubes or non-spherical fullerenes with the ratio of diameterto length larger than one. The planar particles comprise graphite orgraphene platelets with the ratio of thickness to average diameterlarger than one.

In the second aspect, the present invention is the composite material ofintermixed conductive cylindrical and conductive flat carbon particlesobtained by deposition of a suspension (a spray, an ink, a paint, apaste or a coating) containing such particles in any ratio within therange from 1:100 to 100:1 on a substrate. The chemically compatiblesubstrates are polyolefins, glass, Pyrex, quartz, and silicon oxides,ceramic, and metal oxide coated contact surfaces (Preferred oxides arealumina, titanium dioxide, zinc oxide and silicon oxide).

In one specific embodiment, the present invention is a composite formedby drying a suspension comprising planar conductive particles, andtubular conductive particles in a solvent or a matrix. Preferably, thetubular conductive particles are carbon nanotubes and planar conductiveparticles are graphite particles. The suspension comprises the planarand the tubular particles and solvent, and the particles are conductiveparticles with the aspect ratio larger than one. Preferably the aspectratio is much larger than one.

In a prophetic embodiment, the present invention is a compositecomprising interspersed carbon nanotube particles and grapheneparticles. Preferably, carbon nanotubes particles are particles withlength not exceeding 100 nm and length to diameter ratio larger thanone. Additionally, the graphene particles are particles with thediameter not exceeding 100 nm and the thickness to diameter ratiosmaller than one. The smallest dimension of the composite does notexceed the largest average dimension of the conductive carbon particle.

In a third aspect, the present invention is the composite and asubstrate for manufacturing resistors functioning as temperaturesensors.

In a fourth aspect, the present invention is the composite and asubstrate for manufacturing capacitors functioning as temperaturesensors.

In a fifth aspect, the present invention is the composite and asubstrate for manufacturing antennas functioning as temperature sensors.

In a sixth aspect, the present invention is the composite and asubstrate for manufacturing temperature sensors for nanosensor arrays.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and areincluded to further demonstrate certain aspects of the presentinvention. The invention may be better understood by reference to one ormore of these drawings in combination with the detailed description ofspecific embodiments presented herein:

FIG. 1 illustrates the negative thermal coefficient of multiple deviceson glass substrates.

FIG. 2 illustrates the magnitude of the thermal sensitivity of the 1:1multiple wall carbon nanotube (MWCNT) and graphite platelets compositedeposited on low-density polyethylene (LDPE) of the Example 1.

FIG. 3A and B illustrate the construction of the resistive thermometerof the Example 1 whose thermal characteristic is displayed in Table 1.

FIG. 4A and B illustrate the effect of MWCNT-Graphite composite loadingon the temperature coefficient of resistance.

FIG. 5 illustrates the polarization of Raman spectra of theMWCNT-Graphite composite on polyethylene substrate.

FIG. 6 illustrates the lack of polarization of Raman spectra of theMWCNT-Graphite composite on glass substrate.

DETAILED DESCRIPTION

The present invention makes use of new composition of conductive carbonparticles for preparation of electric temperature sensors. Thecomposition allows the manufacturing of conductive carbon compositessuitable for temperature measurement. Such composites are shown as aviable material for fabrication of resistive temperature sensors. Thecomposite composition allows for scaling the size of CNT-graphitetemperature sensors to that the size of other carbon nanotube ensemblebases sensors assuring compatibility of such temperature sensors withfabrication of nanosensor arrays. As temperature is a fundamental andvariable environmental property, incorporation of temperature sensor ina sensor array increases usefulness of an array. This new compositionleads to fabrication of temperature sensors in a simpler and lower costprocedure, as compared to other methods. In addition, the use ofcarbon-based coatings compositions with predictable thermal response ofconductivity further allows prediction of change in EMI shieldingeffectiveness of carbon based coatings, thus increasing value in use ofconductive carbon based composites. As combustible, such materialsrepresent much simpler disposal requirements.

In order to obtain a composite, an intimate mixture of particles isformulated by mixing with any of the common mixing methods. The intimatemixture of particles is suspended in any of the common solvents or acommon solvent mixture by any of common methods. The suspension ofparticles is applied by any means in the desired amount to a substrateand allowed to solidify into the composite by natural or forced solventevaporation. To obtain the composite with useful response ofconductivity to temperature, the intimately intermixed particlescomprise carbon nanotube and graphite particles, carbon nanotubeparticles having aspect ratio of length to width larger than one andgraphite particles having aspect ratio of diameter to thickness largerthan one. In preferred embodiment of the present invention, the averagelength of carbon nanotubes is no smaller than 25 nm. The averagediameter of conductive planar particles is of the same order ofmagnitude as the average length of the carbon nanotubes.

In a preferred embodiment the composite is prepared by use of acomposite material containing suspension of a mixture of conductivegraphite platelets and carbon nanotube particles in a solvent. Thesolvent may comprise a solvent mixture. The composite material may alsocontain binder and other optional ingredients, for example analyticalchemical reagents, surfactants, viscosity modifiers, and dyes orpigments with the limitation to these that do not chemically interactwith the mixture to the extent changing the temperature coefficient ofthe electrical resistance of the resulting material. If these componentswere to disturb the temperature response of the temperature sensor, suchmaterials must be separated from the temperature sensor by a protectivelayer of the compatible material. The mixture of conductive graphiteplatelets and carbon nanotube particles may contain as little as, orless than 5% graphite by weight, the conductive particle balance beingnanotubes. Wherein a nanotube is a hexagonal lattice of carbon rolledinto a cylinder (a nanotube is defined by its diameter, length, andchirality, or twist. Besides having a single cylindrical wall (singlewall nanotubes, or SWNTs), nanotubes can have multiple walls (multiplewall nanotubes, or MWNTs)—cylinders or scrolls inside the othercylinders or scrolls). Aggregates otherwise known as bundles of eithersingle wall nanotubes or multiple wall nanotubes may also be used.

It is not excluded that even less than 5% of planar graphite particlesin the particle composition will suffice for fabrication of adequatetemperature sensors, however other than approximately cylindrical orplanar carbon particle shapes are deemed detrimental to achievingtemperature sensing conductive carbon composites.

Examples of low molecular weight, highly volatile solvents include:water, ethers, alcohols, ketones, hydrocarbons, halogenatedhydrocarbons, preferably C1 to C16, more preferably C1-C10, and mixturesthereof. Examples of alcohols include methanol, ethanol, isopropanol,perfluoropropanol, 1-butanol, 2-butanol, 2-butoxyethanol and octanol.Examples of ketones are acetone, methylethylketone, diethyl ketone.Examples of hydrocarbons include hexane, heptanes, octane, nonane, anddecane, dichloromethane, chloroform, 1,1,1-trichloroethane,trichloroethylene, tetrachloroethylene, benzene, toluene, xylene,1,2,4trimethylbenzene, phenol and naphthalene.

Examples of classes of binders include polyalkylenes, polyalkyleneglycols, polyalkylene alcohols, polyalkylene ketones, polyalkyleneesters, and copolymers or mixtures thereof. Specific examples of bindersinclude polyethylene, polypropylene, polyvinyl alcohol, cellulose andcellulose derivatives, polysaccharides, polystyrene, and mixtures orcopolymers thereof.

Example supports include insulators such as: paper, glass, ceramics,polymers and plastics, polyethylene and other polyolephins, as well aswood, and knit, woven, and non-woven natural and synthetic fibrousmaterials.

In a resistance thermometer embodiment the solid support has electricalconnections placed before or after the deposition of the thermometriccoating. The electrical connections can be of any conductive materialproviding electrical contact with the thermometric composite, such thatthe contacts' and the leads' resistance is smaller than that of thecomposite, preferably two or more orders of magnitude smaller than theresistance of the thermometric composite.

In any of the above-enumerated and future embodiments, the sensingelement, that is the thermometric composite on a support is enclosed orencapsulated in a protective enclosure or an inert layer. Such enclosuremust effectively eliminate other than temperature influences onelectrical resistance of the sensing element. These influences typicallyinclude pressure, light, and most importantly humidity and chemicalexposures. The enclosure protects against degradation of the activetemperature sensing elements to insure reproducible sensing.

In embodiments requiring electrical connections, such connections areincorporated and accessible to couple to a device for detecting aquantity indicative of electron transfer along the CNT-graphite basedcomposite.

It is envisioned that mixtures of approximately planar and approximatelycylindrical particles of other conductive or semiconductive materials invarying ratios will exhibit useful thermometric properties.

It is envisioned that orientation of the particles in the thermometriccomposite may affect the useful temperature range or sensitivity ortemperature range and sensitivity of such composite. In the preferredembodiment the particles are randomly distributed within the composite.

The composites described above may be used to manufacture, for example,smart coatings, electronic components, electrodes, displays, andelectromagnetic interference (EMI) protective and antistatic devices.Moreover, these materials are particularly useful for the manufacture ofnanothermometers, resistance thermometers, temperature sensors andtemperature sensing components of sensor arrays.

For example, a one to one by weight mixture of multi wall CNT (e.g.,MWCNT O.D.×I.D. 40-70 nm×5-40 nm×0.5-2 μm) and graphite is mixed intothe composite material. Such weight ratio of graphite particles ofaverage diameter approximating the average length of the CNT particlesassures that the total area of the planar particles is of the same orderof magnitude as the product of the number of tubular particles presentand of the area established by the mean square radius of gyration of thetubular particles. The resulting composite material is applied to anarea of the substrate between and including terminals of electricalconnectors already on the substrate. In this example, glass is thesubstrate and copper wires are the electrical connectors (FIG. 3). Theconductive carbon composite is cured with one or a combination of theexisting methods [Kirkor].

Subsequently, the composite is sealed in low-density polyethylene(LDPE). The thermal response of the resistance of the composite iscalibrated against traceable temperature standard, in this case a K typethermocouple. Using a DC voltmeter, the resistance can be measured andconverted to temperature. The temperature calibration of a series ofsuch devices is presented in FIG. 2.

The temperature range of the device of the Example 1 is limited by thethermal properties of the encapsulating material, not the carboncomposite.

Graphite exhibits thermal stability to a very high temperature. (Atleast up to 1600 ° C.) Carbon nanotubes are thermally stable at least to400° C., the lowest threshold for CNT oxidation in air. Purcell et al.[Purcell] demonstrated that a MWCNT emitter could be heated by itsfield-emitted current up to 2000 K and remain stable. Still resistiveheating of individual MWCNT at or above 900K might cause shell breakdownand layer ablation at 200-microampere currents [J. Y. Huang 2005 &2006]. It is demonstrated here that CNT-graphite mixtures can serve astemperature sensing materials at least up to 400° C. and envisioned thatprobably well above 400° C. (FIG. 4B) depending on the protectiveenclosure.

Certain continuous inkjet (CB) printers (Amir Noy, SGIA Journal, FirstQuarter 1999, pp. 31-33) can handle inks with large particulates thatwould clog the nozzles of typical inkjet printers. Thus, conductivecomposite materials containing carbon particles such as mixtures ofgraphite platelets and carbon nanotubes may also be used for printing oflow cost, carbon based temperature-sensing devices.

EXAMPLES

1) Formulation of composite material for manufacturing of a paintedresistive thermometer:

A 10 mg of multiwall carbon nanotubes (average length 0.5 to 2 micron)were added to 50 mg of a composite material containing 20% by weight ofcolloidal graphite platelets dissolved in isopropanol with smallquantities of ketones and cellulosic binder. The weight ratio ofgraphite and CNT in the composite material was thus established as 1:1.The modified composite material was painted in approximately 0.5 cmwide, 50 micron thick, and 0.5 cm to 4 cm long traces on a glasssubstrate. The composite was left to dry in ambient air for severalhours. Stable at room temperature conductivity of the composite samplesindicated completion of the drying. Copper wire electrical connectorswere affixed to the opposite ends of each carbon composite with theconductive silver (Ag) paint. The silver paint was allowed to fully cureaccording to its manufacturer's recommendation. The carbon composite onsupporting glass and the Ag paint traces were sealed in LDPE leavingcopper leads exposed. The device was placed in contact with a thermalbath of measured temperature and its resistance measured with a DCvoltmeter. Each device was tested in two cycles of increasing anddecreasing temperature in range from −80 to +110 ° C. Table 1 containsresistance values (Ohms) measured for six thermometers.

TABLE 1 Average measured resistance values (Ohm) at specifiedtemperatures (° C.) for eight temperature sensitive conductivecomposites, GC(1) through GC(*), comprising graphite platelets andMWCNT. The 0° C. * column contains interpolated data assuming theArrhenius type temperature function. T G&C G&C G&C G&C G&C G&C G&C G&C[° C.] (1) (2) (3) (4) (5) (6) (7) (8) 110  401 467 698 673 1115 13641985 2901 100  412 503.2 712 692.3 1140 1405 2041 2931 85 447 516 749727 1166 1442 2074 2998 75 457 521 753 830 1170 1451 2092 3023 60 463526 756 842 1177 1458 2131 3074 56 471.6 539 762 890 1198 1488 2156 308055 470 541 767 970 1205 1493 2164 3095 50 476 544 772 1003 1210 15102176 3100 36 473 544 772 1029 1162 1581 2128 3173 30 481 556 786 10871245 1549 2252 3189 28 482.5 561 792 1085 1260 1573 2272 3270 21 577 615873 1008 1200 1651 2335 3300 19 592 622 889 1013 1208 1667 2339 3450  0*673 908 871 1013 1318 1646 2351 3392  −13.1 694 1140 923 1148 1390 17132575 3600  −15.5 717 1155 978 1154 1400 1749 2599 3640 −45  1032 22001000 1227 1588 1845 2717 3832 −70  1625 3164 1047 1257 1687 1861 28463938 −80  1798 3442 1249 1247 1768 1961 2900 4010The resistance change is proportional to the original device resistanceand the resistance decreases with increasing temperature mimickingsemiconductor behavior. Additionally, the devices demonstrate negativetemperature coefficients. The graphical results plotting resistanceversus temperature for 5 typical devices are shown in FIG. 1.

2) Quantifying the temperature sensitivity of the painted graphite-CNTcomposites. The graphite-CNT 1:1 coatings were painted on polyethylene,equipped with metal connectors, and placed in a glove bag filled withdry air. Radiant heat source was also placed in the same bag, while a Ktype thermocouple led to an outside Fluke 52 temperature meter wasattached to the polyethylene support under the carbon composite. Theconnectors to the painted resistors extended outside the bag to theFluke 75 DC voltmeter. The resistivity of the composites and thetemperature registered with the thermocouple were simultaneouslyrecorded with digital photography. The temperature range was from 20° to60° C., narrow enough for linear approximation of the resistance changewith temperature. The average calculated resistance at 0° C., R0, andthe slope of the resistance are displayed in Table 2 and plotted in FIG.2.

TABLE 2 Resistance and slope data as plotted in FIG. 2. Resistor R0Slope r1 1383.4 −1.63 r2 1781.2 −1.8 r3 2022.7 −1.85 r4 2532.4 −2.27 r52856.8 −2.79 r6 3372.5 −3.68 r7 4513.5 −4.28

The temperature sensitivity of these composites was calculated accordingto the formula (dR/R)(dT/T). The sensitivity coefficient exhibited bythe composites is comparable to the results obtained with graphitethermometers at cryogenic temperatures.

Composite material consisting of MWCNT and graphite in 1:1 and 5:1 ratioby weight was painted in approximately 0.5 cm wide, 50 micron thick, and0.5 cm to 4 cm long traces on a glass substrate. The samples weresubjected to high temperatures ranging from 360-580K for the 1:1 and670-780K for the 5:1 ratios respective as seen in FIG. 4, A and B. Thechange in resistance with temperature is significantly less for thedevice with the larger MWCNT ratio (FIG. 4, B). This is a demonstrationof temperature sensitivity tuning by variation in composite materialcomposition.

3) Composite material consisting of graphite and CNT as previouslydescribed was painted in approximately 0.5 cm wide, 50 micron thick, and0.5 cm to 4 cm long traces on a polyethylene substrate and on glass.

The G band of the Raman spectra of the composite of composite materialcontaining CNT and Graphite on polyethylene are polarized, FIG. 5. The Dband (˜1320 cm-1) is expected to be isotropic, so this is taken as aninternal intensity standard and normalized to one. The intensities ofthe G bands (˜1580 cm-1) of the MWCNT and of graphite excited by p vs. spolarized light reveals the presence or absence of orientation in thecomposite material with these interpenetrating components. More of theMWCNT and graphite respond to the s polarized light than the p at the Gband indicating that the MWCNTs and graphite are aligned lengthwise tothe s-polarized light. Thus, both MWCNT and graphite are oriented in thelayer of the composite. This alignment occurs on oriented polymericsubstrates without external influence or special processing. Theconductive carbon particles in the thermometric composite on glass, thatis, on an amorphous substrate, display no alignment in the Ramanspectra, FIG. 6. This MWCNT and graphite alignment is expected in thesamples quantified for temperature sensitivity, as the same components,mixture ratios and deposition techniques were used.

4) Prophetic Example. Preparation of a resistive temperature nanosensor.The thermometer from the Example 1) is prepared by scaling downtemperature sensing composite size by dispensing onto a preparedsubstrate about a picoliter of appropriately diluted composite materialcontaining the preferred planar to tubular conductive particle ratio andby flash evaporation of the solvent. The surface of the support would bealready equipped with pre-deposited electrical connectors to a readoutdevice.

Such nanodevices could be conveniently mass-produced by ink-jetprinting. It is envisioned that technologies similar to DIP Pentechnique are capable to deposit nanosize composites suitable for thetemperature sensing. The resulting composites are used individually orin multisensor arrays for determining the temperature.

1. A conductive carbon composite material comprising of a cylindricalform of conductive carbon with an aspect ratio larger than one and aplanar form of conductive carbon with an aspect ratio larger than one,the two forms of conductive carbon dispersed in one another in the massratio from 1:100 to 100: and preferably in a mass ratio close to 1:1 andsupported by a compatible substrate. The compatible substrates aresurfaces of aliphatic hydrocarbons, polyolefins, alcohols and polyols,cellulose
 2. (canceled)
 2. The formula of claim 1, wherein averageplanar particles diameter is of the order of the average length of thetubular particles.
 3. The formula of claim 1, wherein the tubular andplanar conductive particles are in any ratio in the composite material.4. The formula of claim 2, wherein the total area of the planarparticles is of the same order of magnitude as the product of the numberof tubular particles present and of the area established by the meansquare radius of gyration of the tubular particles.
 5. The formula ofclaim 3, wherein planar particles are graphite and tubular particles arecarbon nanotubes.
 6. The formula of claim 3, wherein tubular particlescomprise single wall carbon nanotubes.
 7. The formula of claim 3,wherein tubular particles comprise multiple wall carbon nanotubes. 8.The formula of claim 3, wherein the composite material further comprisesa binder.
 9. The formula of claim 3, wherein planar particles areselected from the group that consists of metals and conductive polymersand tubular particles are carbon nanotubes.
 10. The formula of claim 9,wherein tubular particles comprise single wall carbon nanotubes.
 11. Theformula of claim 9, wherein tubular particles comprise multiple wallcarbon nanotubes.
 12. The formula of claim 9, wherein the compositematerial further comprises a binder,
 13. The formula of claim 9 whereintubular particles are selected from the group consisting ofsemiconductors and conductive polymers.
 14. The formula of claim 13,wherein the ink further comprises a binder.
 15. The formula of claim 3can be connected by two conductors.
 16. The resistance decreases withincreasing temperature for the two terminal device of claim
 15. 17. Theanisotropic particles of formula of claim 3 are oriented with respect toeach other in the ink matrix.
 18. The orientation of the anisotropicparticles of formula of claim 3 occurs at deposition without externalmotivation or processing,
 19. The ratio of particles in claim 1 affectsthe temperature sensitivity of the two terminal device in claim
 15. 20.Increasing the ratio of tubular to planar particles in claim 1 above aratio of 1:1 decreases the temperature sensitivity of the two terminaldevice in claim 15.